Fluid pressure mechanism



Oct. 2, 1945. w. A. EATON FLUID PRESSURE MECHANISM.

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' ATTORNEY Patented Oct. 2, 1945 system.

UNITED STATES. PATENTVO'FFICE FLUID PRESSURE MECHANISM Wilfred A. Eaton,Elyria, Ohio, assignor to Bendin-Westinghouse Automotive Air BrakeCompany, Elyria, Ohio, a corporation of Delaware I Application August 4,1943, Serial No. 497,386

1: Claims. (01. 230-2) well above atmospheric pressure, this mode ofoperat'ion permitting the compressing oi fluid at a relatively highpressure at the output side oi the compressor without resulting in acorre sponding. increased pressure ratio, such as would 1 l occur in theevent such a high pressure were ob" tained from a single stagecompressor in the Ordinary manner. It has previously been proposed toemploy systems of this general type, but

some of these systems have required complicated and expensive mechanismfor controlling the pressures in the low ,and high pressure portions ofthe system and it is accordingly an object oi the inlet port 01'compressor during this type otoperation.

a further object of the invention is to provide means for preventing theloss 0! fluid pressure irom .the system to atmosphere under allconditions oi. operation.

These and other objects and novelieatures oi the invention will appearmore iully hereinaiter v iromthe following detailed description whenconsidered in connection with V the accompanying drawing. whereinoneembodiment oi the invention'isillustrated. p a It isto be expresslyunderstood, however-.1 that. the' drawing is employed iorpurposes ofillustration only and isnot designed as a definition of the presentinvention to provide mechanism for overcoming these difllculties. V

Previous mechanisms of the above nature have in some cases necessitatedcontinuous operation of the compressor against a relatively highpressure even when the desired pressures were established in the low andhigh pressure portions of the system, and it is accordingly a furtherobject of the present invention to provide. means con the liimts oi theinvention, reference being had for, this purpose to the appended claims.

ln the single drawing. there is illustrated diagrammatically andpartially in section, a fluid pressure supply system constructed inaccordance withv the principles of the present inventiori. l The systemis provided with low and high pressure reservoirs I and I respectively,together with a fluid compressor 48, whichgmay be or any wellknown type.the compressor being provided. with a discharge connection 8 and aninlet connection Ill, theilatter being adapted to receive fluid fromthe-atmosphere through amonduit II, a conduit trolled by variations oipressure in the system for I unloading the compressor and preventing thecompression of further fluid when the desired pressures are established.

Yet another object 01' the invention is to provide means controlled byvariations or pressure in the low pressure portion otthe system forcontrolling the operation of the compressor to alternately compressatmospheric fluid and supply it to the low pressure portion of thesystem and to recompress fluid from the low pressure portion of thesystemand supply it to the high pressure portion of the system. togetherwith means controlled by variations oi pressure in thehigh pres+ sureportion of the system for rendering the cornpressor ineffective to supplfurther fluid pressure to the system when predetermined desiredpressures are reached in the various parts of the Still another objectof the invention is to provide in a system or the above type. simple andefliclent means for connecting the discharge port I: connected therewithand a one weychech valve is having a connection It with atmosphere. itbeing understood that the check valveis so constituted as to permit theflow oi fluid pressure from the atmosphere to the inlet port or thecompressor and to prevent the flow oi fluid pressure in the oppositedirection through said connections. The outlet port 8 of the compressoris connected with the low pressure reservoir through. a conduit l5 and aconduit II, the latter conduits being connected as shown by means ofacoritrol valve mechanism H to be more fully described hereinafter. Inorder that fluid presvoir I from the compressor, the conduit" isconnected with the latter reservoir by means of conduits l8 and It, thelatter being connected by means of a one way check valve 20, soconstituted as to permit the flow or fluid pressure from the conduit :IIto the conduit is and. to prevent opposite direction.

oi the compressor with the inlet port of the coinpressor and to preventthe flow oi fluid pressure from the high pressure portionof the systemto The valve mechanism ii is provided with a casing 21, the casing beingprovided with a chamber 22 connected with the conduit It, a

chamber .23 connected with the low pressure reservoir and a chamber 24connected with the conduit i8. The chamber 23 is separated from thechamber 22 by means of a partition 25 provided with a centrally locatedport 26, while the chamber 24 is separated from the chamber 22 by meansof a partition 21 provided with a centrally located port 28. The lowerend of the port 25 is normally closed by means of a va ve 29 P videdwith an upwardly extending stem 30 slidably mounted in a partition 3|serving to-deflne the upper end of the chamber 24. A suitable diaphragmor pressure responsive member 32 suitably attached to the upper end ofthe valve stem 30 and clamped between the casing 2| and a cover plate33, as shown, the plate being bolted to the casing by means of bolts 34.The diaphragm serves to define in connection with the casing and coverplate, an atmospheric chamber 35 below the diaphragm and a controlchamber 36 above the diaphragm, a spring 31, interposed between thelower face of the diaphragm and the upper surface of the partition 3|,serving to normally maintain the valve and diaphragm in the positionshown. It will thus be seen that with the parts of the valve I! in theposition shown. the valve serves to establish communication betweenconduits l and I6 through chamber 22, port 26 and chamber 23, and toprevent communication between conduits l5 and I8, while on downwardmovement of the valve in response to the supplying of fluid pressure tothe control chamber 38. the valve operates to close the upper end of theport 26 to prevent communication between con-.

governor 38' to dis-establish the connection beduits l5 and I6, and toopen the port 28 in order to permit communication between conduits l5and I8 through chamber 22, port 28 and chamber 1 24. In order to insureproper action of the diaphragm 32, the chamber is provided with anatmospheric port 38.

In order to control the operation of'the valve mechanism II, a governorof well-known type designated as 39 is associated with the low pressurereservoir, being connected with the reservoir by means of a conduit 40and with the control chamber 36 by means of a conduit 4|, it beingunderstood that the governor is so constructed as to normally preventcommunication between conduits 40 and 4| and to permit communicationbetween conduit 4| and an exhaust port, not shown, an increase in thepressure supplied to the governor through the conduit 40 beyond apredetermined value serving to operate the latter to preventcommunication between the conduit 4| and the exhaust port and toestablish communication between conduits 48 and 4| in order tosupplyfluid pressure from the reservoir to the control chamber 36, withconsequent movement of the valve 20 to the downward position previouslydescribed.

It will be understood from the foregoing description that the dischargeport 01' the'compressor is normally connected with the low pressurereservoir and disconnected from the high'pressure reservoir, and sinceit is an object of the invention, when a predetermined pressure has beenestablished in the low pressure reservoir, to utilize the fluid in thisreservoir to supercharge the compressor by feeding this fluid back intothe inlet of the compressor and recompressing this fluid into the highpressure reservoir at a relatively high pressure, means are alsoprovided under the control of the governor 39 for establishing a 7connection between the low pressure reservoir and the inlet of thecompressor at the same time that the valve mechanism I7 is actuated bythe tween the discharge port and the low pressure reservoir and toestablish a connection between the discharge port of the conduit leadingto the high pressure reservor". The low pressure reservoir isaccordingly connected with the conduit ll leading to the inlet port ofthe compressor by means of conduits 42 and 43, these conduits beinginterconnected by means oi a control valve mechanism 44. The controlvalve mechanism 44 is provided with a casing 45 having an inlet chamber46 and an outlet chamber 41, these chambers being separated by means ofa partition 48 formed in the casing as shown, and provided with acentrally located port 49. The upper end of the port is normally closedby means of a valve element '50, .this valve element being provided witha. downwardly extending stem 5| slidably mounted in a partition 52 whichserves to define the lower end of the chamber 41. A suitable diaphragmor pressure. responsive member 53 is attached to the lowder end of thevalve stem and clamped at its outer periphery to the lower end or thecasing 45 by means of a cover plate 54 attached thereto by means ofsuitable bolts 55. The diaphragm thus serves in connection with thecasing and cover plate to define an atmospheric chamber above thediaphragm having an atmospheric port 51, as well as a control chamber 58below the diaphragm, the control chamber being connected with the outletconduit 4| of the governor 33by means of a conduit 58. The valve isnormally maintained in the position shown by means of a spring 60interposed between the lower face of the partition 52 and the uppersurface of the diaphragm 53, a shoulder or stop 8| formed on the valvestem as shown serving to limit the upward travel of the valve in orderto prevent the possibility of the latter or the valve 44, the resultbeingthat. on o'pera tion of the valve II to dis-establish-thqconnection between the discharge port of the cdinpressor and the low pressurereservoir and to establish a connection between the discharge port andthe conduit leading to the high pressure reser-.

voir, the valve mechanism 44 will simultaneously operate to establish aconnection between the low pressure reservoir and the inlet port 01' thecompressor through the conduit 42, the inlet chamber 48, the port 49,the outlet chamber 41, and conduits 43 and II. Thus on operation of thecontrol valve II to connect the discharge port of the compressor withthe high pressure reservoir, the valve 44 will be eiiective to supplyfluid pressure from the low pressure reservoir to the inlet of thecompressor at a pressure considerably above atmospheric, permitting arelatively high pressure to be delivered to the high pressure reservoirwith the compressor operating at a subit will also be understood that asthe pres- ,sure in the low pressure reservoir decreases, a point will bereached such that the governor 66 will become effective to againdis-establish the connection between conduits l0 and 4| and to establisha connection between the conduit 4| and atmosphere, this resulting in anexhaust of fluid pressure from the control chamber 36 of the valve IT aswell as the control chamber 68 of the valve 44, with a resultant returnof the valves 26 and 56 to the positions shown, whereupon the compressorwill draw in fluid from atmosphere and compress it into the low pressurereservoir in order to replace the fluid supplied to the compressor fromthe low pressure reservoir for supercharging purposes.

It will be obvious that during the operation of a system of theabovedescribed type, it will be necessary to provide means of some formto limit the pressure developed in the high pressure reservoir'to a safeandpredetermined value, and while a safety valve of the conventionaltype might be utilized to'discharge the excess fluid to atmosphere, thistype of operation would result in the loss of fluid from the system withthe rev sultant' necessity of drawing a correspondin I amount ofadditional fluid through the atmospheric intake of the compressor, andsince the fluid in'the atmosphere normally contains a considerableamount of moisture or water vapor,'

this type of operation tends to increase the moisture content in thesystem and to eventually result in excessive precipitation of moisturewithin the system, with a resultant tendency towardthe formation of iceduring low temperature operation which might tend to seriouslyinterfere- .with the safe and satisfactory operation of the mechanism.To this end, means are also.pro-- vided for limiting thepressuredeveloped in the high pressure reservoir without exhausting the excessfluid to atmosphere and this means is also utilized to unload thecompressor in order to prevent the pumping of fluid to either of thereservoirs when the pressure in the high pressure reservoir isestablished at a predetermined value, such unloadingmechanism'including' a conduit 62 connected at one end with the conduitl6 and at the other end with the conduit 43 through the medium of avalve mechanism 66. The valve mechanism 63 provided with a casing 64having an; inlet 0 amber 65 a d an outlet cham r 66 formed t erein, thein ct chamber being connected with the conduit 62 and the outlet chamberbeing connected with theconduit 63. The chambers are separated by meansof a partition .61 having at port 68 centrally located therein, this'port normally being closed by eans of a valve 66 provided with anupwardly extending stem 'lll slidablymounted in a partition ll formed inthe casing ,and serving to define the upper end of the outlet chamber66. The upper end of the valve stem is provided with a diaphragm 12suitably attached thereto and clamped at the periphery thereof to theupper end of the casing by means of a cover plate 13 suitably bolted.thereto. The diaphragm serves in connection with the casingand thecover plate to deflne an atmospheric chamber 16 below the diaphragmconnected with atmosphere by means of a port 15, as well as 5a controlchamber 16 above the diaphragm. The valve is normally maintained in theposition shown by means 01 a spring 'Il interposed between the lowerface of the diaphragm and the upper surface of the partition H, downwardmovement of the valve from. 75

-manner as the governor 39.

assaoso w t 3 the position shown being limited by means of a stop 16formed on the stem of the valve in order to prevent the possibility ofthe valve being forced downward sufl'lciently to close the upper end ofthe conduit connected with the chamber 65.

The supply of fluid pressure to the control charm ber 16 is controlledby the operation of a governor I9, which may be constructed in the sameThe governor is connected with the reservoir 1 by means of a conduit 80and withthe control chamber 16 by means of a conduit 8|, the governorserving normally to establish a connection between the conduit BI andatmosphere and to prevent communication between conduits 86 and 8|, andserving when the pressure in the reservoir 1 exceeds a predeterminedvalue for which the governor may be adjusted, to dis-establishcommunication between conduit BI and atmosphere and to establishcommunication between conduits 86 and BI to supply fluid pressure fromthe reservoir to the control chamber 16. The governor 16 is preferablyso adjusted as to operate at a considerably higher pressure than thegovernor 36. As stated heretofore, the system isso arranged that thecompressor is initially operative to charge the low pressure reservoirto a predetermined pressure, and to thereafter alternately transferfluid from the low pressure reservoir to the high pressure reservoir andfrom atmosphere to the low pressure reservoir to replace fluid which hasbeen transferred therefrom to the high pressure reservoir. Thecompressor is thus alternately operative to supply fluid to the low andhigh pressure reservoirs and as this operation continues,

the pressure in the high pressure reservoir will increase to a valuesumcient to actuate the governor I6 to dis-establish the connectionbetween conduit {6| and atmosphere and to connect the 66 will be moveddownward to establish a connection between conduits 62 and 63, thusserving to connect the discharge port of the compressor with the inletport of the compressor through conduit II, the valve mechanism l7.conduits i6 and 62, chamber 66 of the valve 63, port 61, outlet chamber66, and conduits and II, any fluid pumped by the compressor thus beingreturned to the inlet side of the compressor and serving to maintainboth the inlet and outlet ports at substantially the same pressure inorder to prevent the further supplying of fluid to either of thereservoirs. In order to prevent the possibility of the high pressurefluid in the reservoir 1' from flowing to the conduit 62 and thence tothe inlet port of the compressor through the above describedconnections, the one way check valve 26 interconnecting the conduits i6and I6 is provided, and serves eflectively to prevent loss of fluid fromthe high pressure reservoir when the compressor is unloaded by theaction of the valve 63 under. the control oi the governor 16. In theevent fluid is utilizedi'rom the high pressure reservoir or depleted.therefrom by leakage.- the pressure will eventually drop to such a valuehigh pressure reservoir thatthe governor 18 will again become-operativeto disconnect conduits 80 and 8i and to connect the latter conduit withatmosphere to exhaustfluid pressure from the control chamber 16 andpermit the valve 89 to return to the position shown, thusdis-establishing the connection between the inlet and discharge ports ofthe compressor and permitting the latter to be effective to supply'fluidpressure to oneor the other of the reservoirs dependent on the operationof the control valve II.

The above described system is illustrated as being adapted to supplyfluid for theactuation of a fluid motor 82, this motor being providedwith a piston 83,slidably mounted therein and adapted for connectionwith a device to be actuated, not shown, by means of a conventionalpiston rod 84. Fluid pressure is supplied .to the motor through aconduit 85 connected with the reservoir 1 and a conduit 86 connectedwith the motor, communication between these conduits being controlled bymeans of a brake valve 81, which may be preferably constructed inaccordance with the principles set forth in the patent to Wilfred A.Eaton, No. 2,204,530, dated June 11, 1940. The valve is provided with abrake pedal 88 pivotally mounted thereon by means of a pin 89, and itwill be understood on reference to the above patent, that with the pedalin the position shown, the valve is operative to prevent communicationbetween conduits 85 and 86 and to establish communication betweenconduit 86 and an exhaust port 90, the latter port being connected withthe low pressure reservoir by means of aconduit 9|, while on downwardmovement of the pedal, the valve mechanism is operative to dis-establishthe connection between conduit 86 and the exhaust port 90 and toestablish communication between conduits." and 86 to supply fluidpressure to the motor 82 at a pressure substantially proportional to thedegree of movement of the brake pedal, movement of the pedal back to theposition shown serving to reverse the operation and to exhaust fluidpressure from the motor. In view of the fact that the exhaust port ofthe valve is connected with the lowgpressure reservoir, all fluidexhausted from the motor is returned to the system and is not lost toatmosphere, such fluid being recompressed and deliveredto thehighpressurereservoir. In view of the fact that the low pressurereservoir is normally maintained at a pressure above atmospheric, itwill be understood that this pressure will exist at all times in theconduit 8| and that it will be accordingly necessary to provide a spring92 having sufllcient tension to return the piston 83 to the positionshown against the back pressure in the low pressure side of the systemon release operation of the brake pedal.

There has thus been provided, as heretofore described, a fluid pressuresupply system having a low pressure reservoir preferably maintained at apressure above atmospheric pressure and a maintained at a higherpressure, the delivery of fluid from the compressor to these reservoirsbeing controlled by variations in pressure in both reservoirs in orderto maintain a substantially predetermined relationship between thepressures obtaining. in the two reservoirs. The compressor is initiallyoperated to receive fluid from the atmosphere and to compress it in thelow pressure reservoir, this fluid in turn being returned to the inletof the compressor to supercharge the latter and permit this fluid to becompressed to a higher degree and delivered to the high pressurereservoir. The

aaaepsa compressor operates to alternately supply fluid to one reservoiror the other until such time as the pressure in the high pressurereservoir is sufficient to render the governor and valve mechanismoperative to establish a connection between the discharge port and theinlet port of the compressor, the establishment of this connectionserving unload the compressor and to prevent fur r delivery of fluid toeither of the reservoirs ifistil such time as the pressure conditions inthe system are changed sufliciently to render the governor mechanismoperative to again load the compressor. In view of the fact that nofluid is ,taken into the system after the latter is initially chargedexcept for the purpose of replacing leakage, the concentration of watervapor inthe system can-be maintained at a relatively low value, thusminimizing difllculties which might otherwise occur due to freezing ofsuch moisture in the system. In addition to the '-i; ;'regoing, asinglestage compressor may be utilized to pump a relatively highpressure without rendering it necessary for the compressor to operate atan abnormally high compression ratio with resultant heating of thecompressor parts. These features all contribute'to' a type of operationtending to minimize failures due to freezing and tending to increase thelife of the compressor and minimize the formation of carbon therein.

While one embodiment of the invention has been shown and describedherein with considerable particularity, it will be readily apparent tothose skilled in the art that the invention is not limited to the formshown, but may receive a variety of mechanical expressions. Referencewill, therefore, be had to the appended claims for a definition of thelimits of the invention.

What is claimed is:

1. The combination in a fluid pressure supply system having low and highpressure reservoirs and a compressor provided with inlet and dischargeports, of means for supplying fluid pressure from the compressor to saidreservoirs including a normally open connection between said dischargeport and the low pressure reservoir, a normally closed connectionbetween said discharge port and the high pressure reservoir.

- means including a valve controlled by variations of pressure in saidlow pressure reservoir for closing the flrst connection and opening theother connection when the pressure in said low pressure reservoirexceeds a predetermined value, and means including a valve controlled byvariations in pressure in the high pressure reservoir for establishing aconnection between the second named connection and the inlet port of thecompressor when the pressure in said high pressure reservoir exceeds apredetermined value.

2. The combination in a fluid pressure supply system having high and lowpressure reservoirs and a compressor provided with inlet and dischargeports, of means for supplying fluid pressure from the compressor to saidreservoirs including a normally open connection between the dischargeport and the low pressure reservoir, a normally closed connectionbetween said discharge port and the high pressure reservoir, meansincluding a valve controlled by variations in pressure in said lowpressure reservoir for closing the first connection and opening saidother connection when the pressure in said low pressure reservoirexceeds a predetermined value, means including a valveresponsive tovariations asaaoco in pressure in the high pressure reservoir forestablishing a connection between the second named connection and theinlet port of the compressor when the pressure in said high pressureireservoir exceeds a predetermined value,- and means associated with thesecond named connection for preventing the flow of fluid pressure fromthe high pressure reservoir to the inlet port of the compressor when thesecond named connection is connected with the inlet port of thecompressor. i

3. The combination in a fluid pressure supply system having low and highpressure reservoirs and a compressor provided with inlet and dis chargeports, of means for supplying fluid pressure from. the compressor tosaid reservoirs including a normally open connection between saiddischarge port and the low pressure reservoir, a normally closedconnection between said discharge port and the high pressure reservoir,

means including a valve controlled by variations in pressure in said lowpressure reservoir for closin the first connection and opening saidother connection when the pressure in said low pressure reservoirexceeds a predetermined value, and means including a pressure responsivevalve serially connected between the first named valve e s reservoir andthe inlet port of the compressor, a normally closed connection betweenthe second named connection and the inlet port of the compressor, andmeans for controlling said. connections including valvular meansresponsive to variations in pressure in the low pressure reservoir forclosing the first named connectionand opening the second namedconnection and for opening the connection between the low pressurereservoir and the inlet port when the pressure in the low pressurereservoir exceeds a predetermined value and valvular means controlled byvariations of pressure in the high pressure reservoir for opening theconnection betweenthe second named connectionand the inlet port of thecompressor when the pressure in the high pressure reservoir exceeds apredetermined value. 6. The combination in a fluid pressure supplysystem having low and high pressure reservoirs and a compressor providedwithinlet and discharge ports, of means for supplying fluid pressurefrom the compressor to said reservoirsineluding a normally openconnection between said discharge port and the low pressure reservoir,

a normally closed connection between said discharge port and the highpressure reservoir, a normally closed connection between said secondnamed connection and the inlet port of the compressor, a normally closedconnection between the low pressure reservoir and the inlet port of thecompressor, fluid pressure operated valvular means for controlling thefirst two connections, fluid pressure operated valvular means forcontrolling the third named connection, fluid pressure operatedvalvularmeans for controlling the last named connection, means responsive tovariations in pressure in the low pressure reservoir for operating thefirst named discharge port and the low pressure reservoir,

a normally closed connection between said discharge port and the highpressure reservoir, means including a valve controlled by variations inpressure in said low pressure reservoir for closing the first connectionand opening said other connection when the pressure in said low pressurereservoir exceeds a predetermined value, means controlled by variationsin pressure in the high pressure reservoir for establishing a connectionbetween said second named connection and the inlet port of thecompressor when the pressure in said high pressure reservoir exceeds apredetermined value, and means including a valve controlled byvariations in pressure in the low pressure reservoir for establishing aconnec-,

tion between the latter reservoir and the inlet port of the compressorwhen the pressure in said low pressure reservoir exceeds said first namdpredetermined value.

5. The combination in a fluid pressure supply system having high and lowpressure reservoirs and a compressor provided with inlet and dischargeports, of means for alternately supplying fluid pressure from thecompressor tothe low pressure reservoir and from the low pressurereservoir to high pressure reservoir through said compressor and forpreventing the compressor from supplying fluid pressure to either of thereservoirs including a normally open connection between the dischargeport of the compressor and the low pressure reservoir, a nor-'valvularmeans to close the first named connection and open the secondnamed'connection and for operating the last named valvular means to openthe last named-connection when the pressure in the low pressurereservoir exceeds a predetermined value and for permitting operation ofsaid first and last named valvular means in the reverse direction whenthe pressure in said low pressure reservoir drops to a lowerpredetermined value, and means responsive to variations in pressure inthe high pressure reservoir for operating the second named valvularmeans to open the third named connection when the pressure in the highpressure reservoir exceeds a predetermined value and to close saidconnection when the pres- .sure in the high pressure reservoir drops toa 1 tions in pressure in said low pressure reservoir for closing thefirst connection and opening said other connection when-the pressure insaid low pressure reservoir exceeds a predetermined value, meansincluding a valve responsive to variations in pressure in the highpressure reesrvoir for connecting the second named connection with theinlet port of the compressor when the pressure in the high pressurereservoir exceeds a predetermined value,

valvular means controlled by variations in pressure in the low pressurereservoir for connecting the low pressure reservoir with the inlet portof the compressor when the pressure in said low pressure reservoirexceeds said first named predetermined value, and means for preventingthe flow of fluid pressure from the inlet port of the compressor toatmosphere when said connections are established between said inlet portand said low pressure reservoir and between said inlet port and saidsecond named connection.

8. The combination in a fluid pressure supply system having low and highpressure reservoirs and a compressor provided with inlet and dischargeports, of means for supplying fluid pressure from the compressor to saidreservoirs including a normally open connection between said dischargeport and the low pressure reservoir, a

- normally closed connection between the discharge the pressure in saidhigh pressure reservoir exceeds a higher predetermined value.

9. The combination in a fluid pressure supply system having low and highpressure reservoirs and a compressor provided with-inlet and dischargeports, of means for supplying fluid pressure from the compressor to saidreservoirs including a normally open connection between thedischarge'port and the low pressure reservoir, a normally closedconnection between said discharge port and the high pressure reservoir,a normally closed connection between the low pressure reservoir and theinlet port of the compressor, a normally closed connection between saidsecond named connection and the inlet port of the compressor, valvularmeans controlled by variations in pressure in the low pressure reservoirfor closing the first named connection and opening the second and thirdnamed connections when the pressure in said reservoir exceeds apredetermined value, valvular means controlled by variation in pressurein the high pressure reservoir for opening said last named connectionwhen the pressure in said high pressure reservoir exceeds a higherpredetermined value, and means associated with said second namedconnection for preventing the flow of fluid pressure from the highpressure reservoir to the inlet port of the compressor through saidconnections and second named valvular means.

10. The combination in a fluid pressure supply system having low andhigh pressure reservoirs and a compressor provided with inlet anddischarge ports, of means for controlling the supply of fluid pressurefrom said compressor to said reservoirs for alternately supplying fluidpressure to the low pressure reservoir, for supplying fluid pressurefrom the low pressure reservoir to the high pressure reservoir throughthe compressor,

. and for preventing the supplying of fluid pressure to either of saidreservoirs by the compressor, including a, transfer valve controlled byvariations of pressure in the low pressure reservoir for a1ternatelyconnecting the discharge port of the compressor with the low and highpressure reservoirs respectively, valvular means controlled byvariations in pressure in the low pressure reservoir for alternatelyconnecting and disconnecting the low pressure reservoir with the inletport of the compressor, and valvular means controlled by variations ofpressure in the high pressure reservoir for alternately connecting thedischarge and inlet ports of the compressor through the first namedvalvular means.

11. The combination in a fluid pressure supply system having low andhigh pressure reservoirs and a compressor having inlet and dischargeports, of means for controlling the flow of fluid pressure from thecompressor to said reservoirs including a valve having a connection withthe discharge port, and connections with both of said reservoirs, meansfor normally maintaining said valve in a position to permit the flow offluid pressure from the discharge port to the low pressure reservoir andto prevent the flow of fluid pressure to the high pressure reservoir,means including a pressure responsive member for moving said valve toprevent the flow of fluid pressure from the discharge port to the lowpressure reservoir and to permit the flow of fluid pressure to thehighpressure reservoir when the pressure in the low pressure reservoirexceeds a predetermined value, a connection between the low pressure reservoir and the inlet port, means including a valve for normally closingsaid connection, means including a pressure responsive member for movingsaid second valve to open position when the pressure in said lowpressure reservoir exceeds said predetermined value, and means includinga valve controlled by variations of pressure in the high pressurereservoir for establishing a connection between said discharge port andinlet port through said first named valve when said valve is positionedto permit the flow of fluid pressure from the discharge port to the highpressure reservoir and when the pressure in the latter exceeds apredetermined value higher than the first named predetermined value.

12. The combination in a fluid pressure supply system having low andhigh pressure reservoirs and a compressor provided with discharge andinlet ports, of means for controlling the supply of fluid pressure tosaid reservoirs including a valve operable in one position to connectthe discharge port with the low pressure reservoir and in a secondposition to disconnect the discharge port from the low pressurereservoir and to connect said port with the high pressure reservoir,means including a second valve operable in one position to preventcommunication between the low pressure reservoir and the inlet port andin a second position to establish a connection between the low pressurereservoir and the inlet port, means including a third valve operable inone position to prevent the flow of fluid pressure from the dischargeport to the inlet port and in a second position to establishcommunication between said ports, and means for controlling theoperation of said valves including means responsive to variations ofpressure in the low pressure reservoir for moving said first and secondvalves to the second position when the pressure in the low pressurereservoir exceeds a predetermined value and means responsive tovariations of pressure in the high pressure reservoir for moving saidthird valve to the second position when the pressure in the highpressure reservoir exceeds a higher predetermined value.

13. The combination in a fluid pressure supply means responsive tovariations of pressure in the lowpressure reservoir for moving saidfirst andsystem having low and high pressure reservoirs and a.compressor provided with discharge and with the high pressurereservoinmeans including a second valve operable in one position toprevent communication between the low pressure reservoir and the inletport and in a second position to establish a connection between the lowpressure reservoir and the inlet port, means for I controlling theoperation of said valves including second valves to said secondpositions when the pressure in said low pressure reservoir exceeds apredetermined value. and means for establishing a connection between thedischarge port and inlet port when said first valve is in said secondposition including a third valve connected in serial re lationship withsaid first valve between said ports and means responsive to variationsof pressure in said high pressure reservoir for opening said third valvewhen the pressure in the high pressure reservoir exceeds a higherpredetermined value.

' WIIFRED A. EATON.

